The goal of traffic management systems is to efficiently manage existing transportation resources in response to dynamic traffic conditions. Traffic management tasks are fairly simple, use roads to their optimal capacity. For the past twenty five years the idea of a non-human based system managing traffic has been a goal of the traffic industry. The basis behind it being that a junction or central controller can manage traffic flow significantly reducing congestion and traffic jams within a city and increasing traffic flow.
The inability of existing road networks to cope with increased demand has been identified as one of the most problematic and pressing infrastructure issues. Presently a large number of signal controlled junctions are still controlled by systems based on fixed timed schedules. In more sophisticated systems, remote human intervention is possible so that a person can watch a camera and change the timing schedules from a traffic control centre according to different traffic situations. The first system relies on the assumption that generally the traffic conditions remain relatively constant. The latter system requires continuous human control and prediction. Additionally adaptive urban traffic control systems (UTCS) can be used. Two examples of the UTC-systems are known, namely the SCATS and the SCOOT system.
Many metropolitan areas have created traffic management centres (TMC) with closed-circuit television (CCTV) cameras, traffic and weather sensors, electronic variable message signs (VMS), traffic signals, and ramp meters to monitor and manage traffic flow on streets and motorways, however most of these still rely on data being given to a person who can make a decision based on that data.
The modern goal is to create a system that can hand this responsibly over to an automated traffic signal control system. Typically a central computer is used to generate timing schedules off-line based on average traffic conditions for a specific time of day. The schedules are then downloaded to local controllers at the appropriate time of day. Timing schedules are typically obtained either by maximizing the bandwidth on arterial streets or by minimizing a disutility index, such as a measurement of stops and delays.
The off-line, optimization approach has limitations in responding to unpredictable changes in traffic demand. These systems can respond to changing traffic demand by performing incremental optimizations at the local level. The most notable of these are the “Sydney Coordinated Adaptive Traffic System” (SCATS), developed in Australia, and the “Split Cycle and Offset Optimizing Technique” (SCOOT), developed in England. SCATS is installed in several major cities in Australia, New Zealand, and Asia. SCOOT is installed in a number of other cities.
Both SCATS and SCOOT are complicated, real-time systems that manage large traffic signal networks. These systems provide predetermined, incremental changes in the cycle time, phase split, and offset of traffic signals in their networks. Cycle time is defined as the duration for completing all phases of a signal. Phase split is the division of the cycle time into periods of green signals for the competing approaches. Offset is the time relationship between the start of each phase among adjacent intersections.
SCATS organizes groups of intersections into subsystems. Each subsystem contains only one critical intersection whose timing parameters are adjusted directly by a regional computer based on the average prevailing traffic condition for the area. The basic traffic data used in SCATS is the “degree of saturation,” defined as the ratio of the effectively used green time to the total available green time. Cycle time for the critical intersection is adjusted to maintain a high degree of saturation for the lane with the greatest degree of saturation. Phase split for the critical intersection is adjusted to maintain equal degrees of saturation on competing approaches. All other intersections in the subsystem are coordinated with the critical intersection, sharing a common cycle time and having coordinated phase split and offset. Subsystems may be linked to form a larger coordinated system when their cycle times are nearly equal. At the lower level, each intersection can independently shorten or omit a particular phase based on local traffic demand. However, any time saved by ending a phase early must be added to the subsequent phase to maintain a common cycle time among all intersections in the subsystem. The offsets among the intersections in a subsystem are selected to eliminate stops in the direction of dominant traffic flow.
SCOOT uses real-time traffic data collected by sensors located far upstream from a signal to generate traffic flow models, called “cyclic flow profiles.” Cyclic flow profiles are used to estimate how many vehicles will arrive at a downstream signal when that signal is red. This estimate provides predictions of queue size for different hypothetical changes in the signal timing parameters. The objective of SCOOT is to minimize the sum of the average queues in an area. A few seconds before every phase change, SCOOT uses the flow model to determine whether the phase change should be advanced by 4 seconds, remain unaltered, or be retarded by 4 seconds. Once each cycle, SCOOT also determines whether the offset should be advanced by 4 seconds, remain unaltered, or be retarded by 4 seconds. Once every few minutes, SCOOT determines whether the common cycle time of all intersections grouped in a subsystem should be incremented, unchanged, or decremented by a few seconds. Thus, SCOOT changes its timing parameters in predetermined, fixed increments to optimize an explicit performance objective.
Because prior traffic signal systems that rely on centralized or regional computer control do not respond well to unpredicted changes in traffic demand and become ineffective when the central or regional computer fails, there is a need for an adaptive, serf-organizing, fault-tolerant traffic signal control system that is based on local traffic data and localized computer control.
U.S. Pat. No. 5,357,436, assigned to Rockwell International Cooperation, discloses a traffic signal network controlled by an adaptive, fuzzy logic based, distributed system of microprocessors. However a problem with this system is that it is complex to implement and operates on a staged process. A drawback with the Rockwell system is that the system operates on fixed stages in a single agent architecture. This results in a rigid system that does not provide any flexibility for dynamic traffic monitoring at individual traffic junctions. Other similar published patent literature suffer from the same problems include NL 1018875, WO97/34274 and U.S. Pat. No. 6,317,058.
An object of the present invention is therefore to provide a traffic management system and method to overcome the above mentioned problems.